The release of mercury to the environment from coal-fired power plants, mining, and smelting operations is of special concern since these sources are currently uncontrolled and the use of coal is expected to increase significantly. Mercury which is released into the environment becomes available for methylation. Methylation rates in ecosystems are a function of the mercury burden, bacterial population, and other physicochemical conditions. Analysis of mercury forms in the air around Tampa Bay, Florida revealed that about 21% of mercury in the atmosphere is of methylmercury types. This paper reports a study on the uptake and tissue accumulation of **2**0**3Hg-methylmercuric chloride following oral and inhalation administration in female rats.